Coronary artery disease (CAD) occurs when the coronary arteries that supply blood to the myocardium become hardened and narrowed due to the buildup of atherosclerotic plaque. An atherosclerotic plaque is the site of an inflammatory reaction within the wall of an artery and is made up of a core containing lipid and inflammatory cells surrounded by a connective tissue capsule. A myocardial infarction (MI), or heart attack, occurs when atherosclerotic plaque within a coronary artery ruptures and leads to the clotting of blood (thrombosis) within the artery by exposing the highly thrombogenic lipid core of the plaque to the blood. The complete or nearly complete obstruction to coronary blood flow can damage a substantial area of heart tissue and cause sudden death, usually due to an abnormal heart rhythm that prevents effective pumping.
It is generally accepted that physical activity and fitness improve health and reduce mortality. Studies have indicated that aerobic training improves cardiac autonomic regulation, reduces heart rate and is associated with increased cardiac vagal outflow. Physical conditioning can be considered to be a repetitive, high-level exercise that occurs intermittently over time.
Improved systems and methods for controlling blood flow are needed.